This invention relates to an idle rotation controller for an engine, which can maintain a desired number of revolutions per minute (hereinafter referred to as "RPM") when the engine is idling.
Conventional idle rotation controllers for engines are disclosed in, e.g., Japanese Patent Examined Publications Nos. sho. 49-40886 and 61-53544.
The controller disclosed in the above-mentioned Publication No. sho. 49-40886 operates to adjust the amount of intake air so that the RPM of the engine during idling maintain a predetermined desired value. This controller has a bypass air duct bypassing the throttle valve in the intake system of the engine. In the bypass air duct there is a control valve that controls the amount of air flowing in the duct from the upstream side of the throttle valve to the downstream side thereof. Therefore, the controller controls the amount of air by providing feedback control to the control valve in accordance with the difference between the actual RPM of the engine and the predetermined desired RPM.
The controller proposed in the above-mentioned Publication No. Sho. 61-53544 is disclosed to adjust the ignition timing of the engine to prevent the RPM of the engine from being dropped or varied due to fluctuations in load at idle. This controller employs feedback control in order to maintain the desired RPM of the engine control as well as to prevent variations in RPM. The feedback control is effected by correcting the ignition timing in accordance with the difference between the actual RPM of the engine and the desired RPMs or with the variations in RPM.
The idle rotation controllers thus organized have addressed the following problem. When misfire occurs in one of the cylinders of the engine and the RPMs of the engine varies greatly, a variation in the number of revolutions occurs in the engine due to the feedback control. This subjects the engine to a hunting condition. During the hunting condition, the engine may stop depending on load conditions and operate improperly.